Pretreatment before painting of composite metal structures containing aluminum portions

ABSTRACT

In a process for the chemical pretreatment before painting of composite metal structures that contain aluminum or aluminum alloy portions together with steel, galvanized steel and/or alloy-galvanized steel portions, in a first step the metal structure is treated with a zinc phosphating solution that forms a surface-covering crystalline zinc phosphate layer on steel and on galvanized or alloy-galvanized steel, but without forming a zinc phosphate layer on the aluminum portions, and then in a second step the metal structure is brought into contact with a treatment solution that does not excessively dissolve the crystalline zinc phosphate layer on steel, galvanized and/or alloy-galvanized steel, but forms a conversion layer on the aluminum portions.

This application claims the benefit of provisional application No.60/058,481 filed Sep. 10, 1997.

BACKGROUND OF THE INVENTION

For many reasons, such as weight, rigidity or recyclability, aluminum isincreasingly used in vehicle construction. In the context of thisinvention the expression “aluminum” refers not only to pure aluminum butalso to aluminum alloys whose main component is aluminum. Examples ofcommonly used alloying elements are silicon, magnesium, copper,manganese, chromium and nickel, the total proportion by weight of thesealloying elements in the alloy normally not exceeding 10%. Whereasengine and gear parts, wheels, seat frames, etc. already contain largeamounts of aluminum, the use of aluminum in bodywork construction ispresently still restricted to parts such as hoods, rear trunk lids,inner door parts and various small parts as well as truck cabins, sidewalls of transporters or attachments to minivans. Overall, worldwideless than 5% of the metal surface of automobile bodies is made ofaluminum. The increased use of aluminum in this sector is beingintensively investigated by the aluminum and automobile industries.

This invention relates to a process for the corrosion-preventionpretreatment before painting of composite metal structures that containaluminum and/or aluminum alloy portions in addition to steel and/orgalvanized steel portions. The process is particularly intended for usein automobile manufacturing. In automobile manufacturing, car bodies orcar body parts that contain structural portions of aluminum and/or itsalloys in addition to structural portions of steel and/or galvanizedsteel are subjected to a conversion-chemical pretreatment before theyare painted. In this connection a cathodic electro-dip-coating isconventionally used at the present time as the first painting stage. Theprocess according to the invention is particularly suitable as apretreatment for this stage.

The process differs from previous conventional pretreatment processes inautomobile manufacturing in that a surface-covering zinc phosphate layeris deposited in a first step on the steel and/or galvanized steelsurfaces, without coating the aluminum surfaces to any appreciableextent. A second step comprises a treatment with a solution that doesnot excessively attack the previously formed zinc phosphate layer, andindeed preferably even enhances its corrosion-prevention action, andwhich simultaneously forms a surface layer on the aluminum surfaces.

A two-stage process is thus involved, whose first stage comprises aconventional zinc phosphating. It is a necessary condition, of course,that a zinc phosphating solution is used that does not form a layer onaluminum. Such zinc phosphating solutions are known in the prior art andare referred to by the way of example hereinafter. In the second stagesolutions with constituents that are effective to form a protectivelayer on aluminum are used. In this connection the nature andconcentration of these solutions should be chosen so that on the onehand a layer is reliably formed on the aluminum surfaces, but on theother hand the crystalline zinc phosphation layers formed on the ironand/or zinc surfaces are not excessively damaged.

The aim of phosphating metals is to produce firmly adhering metalphosphate layers on the metal surface that per se already improve thecorrosion resistance, and in conjunction with paints or other organiccoatings contribute to a substantial improvement of the coating adhesionand resistance to creepage under corrosive stress. Such phosphatingprocesses have been known for a long time. For the pretreatment beforepainting, especially before electro-dipcoating, low zinc phosphatingprocesses, in which the phosphating solutions contain relatively smallconcentrations of zinc ions, for example 0.5 to 2 grams per liter,hereinafter usually abbreviated as “g/l”, are particularly suitable. Abasic parameter in these low zinc phosphating baths is the weight ratioof phosphate ions to zinc ions, which is normally above 8 and may reachvalues of up to 30.

It has been found that phosphate layers with substantially improvedcorrosion-prevention and paint adhesion properties can be formed by theco-use of other polyvalent cations in the zinc phosphating baths. Forexample, low zinc processes with the addition of, e.g., 0.5 to 1.5 g/lof manganese ions and, e.g., 0.3 to 2.0 g/l of nickel ions are widelyused as so-called “tri-cation” processes for preparing metal surfacesfor painting, for example for cathodic electro-dipcoating of car bodies.

Since nickel and its alternative cobalt also are classed as hazardousfrom the toxicological and effluent treatment aspects, efforts are beingmade at the present time to find phosphating processes that are just aseffective as the tri-cation processes but employ significantly lowerbath concentrations of nickel and/or cobalt and preferably even dispensewith these two metals altogether.

EP-A-459 541 describes phosphating solutions that are essentially freeof nickel and that contain, in addition to zinc and phosphate, 0.2 to 4g/l of manganese and 1 to 30 milligrams per liter, hereinafter usuallyabbreviated as “mg/l”, of copper. From DE-A-42 10 513 nickel-freephosphating solutions are known that contain, in addition to zinc andphosphate, 0.5 to 25 mg/l of copper ions as well as hydroxylamine asaccelerator. These phosphating solutions optionally also contain 0.15 to5 g/l of manganese.

German patent application DE 196 06 017.6 describes a phosphatingsolution, with a decreased heavy metal concentration, which contains 0.2to 3 g/l of zinc ions, 1 to 150 mg/l of manganese ions, and 1 to 30 mg/lof copper ions. This phosphating solution may optionally contain up to50 mg/l of nickel ions and up to 100 mg/l of cobalt ions. A furtheroptional constituent is lithium ions in amounts of between 0.2 and 1.5g/l.

DE 195 38 778 describes controlling the coating weight of phosphatelayers by the use of hydroxylamine as accelerator. The use ofhydroxylamine and/or its compounds in order to influence the form of thephosphate crystals is known from a number of publications. EP-A-315 059discloses as a special effect of the use of hydroxylamine in phosphatingbaths the fact that on steel the phosphate crystals still occur in thedesired columnar or nodular form, even if the zinc concentration in thephosphating bath exceeds the conventional range for low zinc processes.In this way it is possible to operate the phosphating baths with zincconcentrations up to 2 g/l and with weight ratios of phosphate to zincof as low as 3.7. The required hydroxylamine concentration is given as0.5 to 50 g/l, preferably 1 to 10 g/l.

WO 93/03198 discloses the use of hydroxylamine as accelerator intri-cation phosphating baths with zinc contents of between 0.5 and 2 g/land nickel and manganese contents of in each case 0.2 to 1.5 g/l,specific weight ratios of zinc to the other divalent cations having tobe maintained. In addition, these baths contain 1 to 2.5 g/l of a“hydroxylamine accelerator”, which according to the description denotessalts of hydroxylamine, preferably hydroxylamine ammonium sulfate.

In order to improve the corrosion prevention produced by the phosphatelayer, a so-called passivating post-rinsing, also termedpost-passivation, is generally employed in this technology. Treatmentbaths containing chromic acid are still widely used for this purpose.For reasons of work safety and environmental protection there is atendency, however, to replace these chromium-containing passivatingbaths by chromium-free treatment baths. Organo-reactive bath solutionscontaining complexing substituted poly(vinylphenols) are known for thispurpose. Examples of such compounds are described in DE-C-31 46 265.Particularly effective polymers of this type contain amine substituentsand may be obtained by a Mannich reaction between poly(vinylphenols) andaldehydes and organic amines. Such polymers are described for example inEP-B-91 166, EP-B-319 016 and EP-B-319 017. Polymers of this type arealso used within the scope of the present invention, and accordingly thecontents of the immediately aforementioned four documents, except to anyextent that may be inconsistent with any explicit teaching herein, arehereby incorporated herein by reference. The use of such polyvinylphenol derivatives for the surface treatment of aluminum is known, forexample, from the aforementioned EP-B-319 016.

WO 90/12902 discloses a chromium-free coating for aluminum, the aluminumsurfaces being contacted with a treatment solution that has a pH in therange from about 2.5 to about 5.0 and contains, in addition to polyvinylphenol derivatives, also phosphate ions as well as fluoro acids of theelements zirconium, titanium, hafnium and silicon.

U.S. Pat. No. 5,129,967 discloses treatment baths for a no-rinsetreatment (termed there as “dried in place conversion coating”) ofaluminum, containing:

(a) 10 to 16 g/l of polyacrylic acid or copolymers of acrylic acid,

(b) 12 to 19 g/l of hexafluorozirconic acid,

(c) 0.17 to 0.3 g/l of hydrofluoric acid, and

(d) up to 0.6 g/l of hexafluorotitanic acid.

EP-B-8 942 discloses treatment solutions, preferably for aluminum cans,containing:

(a) 0.5 to 10 g/l of polyacrylic acid or an ester thereof,

(b) 0.2 to 8 g/l of at least one of the compounds H₂ZrF₆, H₂TiF₆ andH₂SiF₆, the pH of the solution being below 3.5,

as well as an aqueous concentrate to replenish the treatment solution,containing:

(a) 25 to 100 g/l of polyacrylic acid or an ester thereof,

(b) 25 to 100 g/l of at least one of the compounds H₂ZrF₆, H₂TiF₆ andH₂SiF₆, and

(c) a source of free fluoride ions that yields 17 to 120 g/l of freefluoride.

DE-C-19 33 013 discloses treatment baths with a pH above 3.5, whichbesides complex fluorides of boron, titanium or zirconium in amounts of0.1 to 15 g/l, measured as its stoichiometric equivalent as boron,titanium, or zirconium as appropriate, additionally contain 0.5 to 30g/l of oxidizing agent, especially sodium meta-nitrobenzenesulfonate.DE-C-24 33 704 describes treatment baths to improve paint adhesion andpermanent corrosion prevention on, inter alia, aluminum, which maycontain 0.1 to 5 g/l of polyacrylic acid or its salts or esters as wellas 0.1 to 3.5 g/l of ammonium fluorozirconate, calculated as ZrO₂. ThepH of these baths may vary over a wide range. The best results aregenerally obtained when the pH is between 6 and 8. U.S. Pat. No.4,992,116 describes treatment baths for the conversion treatment ofaluminum with pH values between about 2.5 and 5, which contain at leastthree components:

(a) phosphate ions in the concentration range between 1.1×10⁻⁵ to5.3×10⁻³ mole/l, corresponding to 1 to 500 mg/l,

(b) 1.1×10⁻⁵ to 1.3×10⁻³ mole/liter, hereinafter usually abbreviated as“mole/l”, of a fluoro acid of an element of the group Zr, Ti, Hf and Si(corresponding to 1.6 to 380 mg/l of each element) and

(c) 0.26 to 20 g/l of a polyphenol compound obtainable by reactingpoly(vinylphenol) with aldehydes and organic amines.

A molar ratio of fluoro acid to phosphate of about 2.5:1 to about 1:10should be maintained.

DE-A-27 15 292 discloses treatment baths for the chromium-freepretreatment of aluminum cans, which contain at least 10 parts permillion by weight, hereinafter usually abbreviated as “ppm”, of titaniumand/or zirconium, between 10 and 1000 ppm of phosphate, and a sufficientamount of fluoride, but at least 13 ppm, to form complex fluorides ofthe titanium and/or zirconium present, and have pH values of between 1.5and 4.

WO 92/07973 discloses a chromium-free treatment process for aluminum,which uses as essential components in acid aqueous solution 0.01 toabout 18 wt. % of H₂ZrF₆ and 0.01 to about 10 wt. % of a3-(N-C₁₋₄alkyl-N-2-hydroxyethyl-aminomethyl)-4-hydroxy-styrene polymer.Optional components include 0.05-10 wt. % of dispersed SiO₂, 0.06 to 0.6wt. % of a solubilizing agent for the polymer, as well as a surfactant.The aforementioned polymer is included among the “reaction products ofpoly(vinylphenol) with aldehydes and organic hydroxyl group-containingamines” described below and that can be used within the scope of thepresent invention.

In practice it has been found that in the joint phosphating of surfacesof aluminum and those of steel and/or galvanized steel, technicalcompromises have to be accepted as regards the composition of thephosphating baths. Aluminum ions released from the aluminum surface bythe etching and pickling action act as a bath poison for the phosphatingsolution and interfere in the formation of zinc phosphate crystals oniron surfaces. The dissolved aluminum must therefore be precipitated ormasked by appropriate measures. For this purpose free or complex-boundfluoride ions are normally added to the phosphating baths.

The fluoride ions mask the aluminum ions by complex formation and/orprecipitate these ions as hexa-fluoroaluminates of sodium and/orpotassium if the solubility products of the corresponding salts areexceeded. Furthermore free fluoride ions usually lead to an increasedetching attack on the aluminum surfaces, with the result that a more orless closed and sealed zinc phosphate layer can form on the latter.

The joint phosphating of aluminum structural portions with those ofsteel and/or galvanized steel thus has the technical disadvantage thatthe phosphating baths have to be very accurately monitored as regardstheir fluoride content. This increases the control and monitoring workinvolved and may require stocking and metering fluoride-containingsolutions as separate replenishment solutions. Also, the precipitatedhexafluoroaluminate salts increase the amount of phosphating sludge andraise the cost of its removal and disposal.

Accordingly there exists a need for pretreatment processes for complexstructural parts, for example automobile bodies, that contain besidesaluminum portions, also steel and/or galvanized steel portions. Theformulation range for the phosphating baths should be broadened and thecontrol and monitoring work involved should be reduced. The result ofthe overall pretreatment should be the formation of a conversion layeron all exposed metal surfaces that is suitable as a corrosion-preventingpaint substrate, especially before a cathodic electro-dipcoating.

SUMMARY OF THE INVENTION

This object is achieved by a process for the chemical pretreatment,before an organic coating, of composite metal structures that containaluminum or aluminum alloy portions together with steel, galvanizedsteel and/or alloy-galvanized steel portions, characterized by:

(I) treating in a first step the composite metal structure with a zincphosphating solution that forms on steel and on galvanized and/oralloy-galvanized steel a surface-covering crystalline zinc phosphatelayer having a coating weight in the range from 0.5 to 5 g/m², butwithout forming a zinc phosphate layer on the aluminum portions;

and subsequently, with or without intermediate rinsing with water,

(II) contacting in a second step the composite metal structure with atreatment solution that does not dissolve more than, with increasingpreference in the order given, 60, 50, 40, 30, 20, 15, 10, 8, or 6% ofthe crystalline zinc phosphate layer formed on steel, galvanized and/oralloy-galvanized steel in step (I), but does produce a conversion layeron the aluminum portions.

The stipulation that no zinc phosphate layer is to be formed on thealuminum portions in the treatment step (a) is to be understood to meanthat no closed and sealed crystalline layer is formed and that the massper unit area of any deposited zinc phosphate does not exceed 0.5 gramsper square meter, hereinafter usually abbreviated as “g/m²”. In order tosatisfy this condition, the phosphating baths may be arbitrarilyformulated as long as specific conditions for the fluoride concentrationare observed. These conditions may be found in EP-B-452 638. Thisdocument summarizes the conditions under which a closed zinc phosphatelayer is formed on aluminum surfaces. According to this disclosure theconcentration of free fluoride ions for example, measured in g/l, shouldsatisfy the condition that, at a specific temperature T (in ° C.), itlies above a value of 8/T. Since however within the scope of the presentinvention no zinc phosphate layer should be formed on aluminum in thephosphating step (I), in contrast to the teaching of EP-B-452 638, at aspecific temperature T (in ° C.) the concentration of free fluoride ions(in g/l) in the phosphating solution must be below 8/T.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, in the phosphating step (I) a zinc phosphating solutionwhich has a pH in the range from about 2.5 to about 3.6 and atemperature in the range from about to about 65° C., and which does notcontain more free fluoride in g/l than is specified by the expression8/T, “T” denoting the bath temperature in ° C., is preferably used.Independently for each component stated, this zinc phosphating solutionpreferably also comprises:

0.3 to 3 g/l of Zn(II),

to 40 g/l of phosphate ions,

and at least one of the following accelerators:

0.3 to 4, or more preferably 1 to 4, g/l of chlorate ions,

0.01 to 0.2 g/l of nitrite ions,

0.05 to 2, or more preferably 0.2 to 2, g/l of m-nitrobenzenesulfonateions,

0.05 to 2 g/l of m-nitrobenzoate ions,

0.05 to 2 g/l of p-nitrophenol,

0.001 to 0.15, or more preferably 0.001 to 0.070, g/l of hydrogenperoxide in free or bound form,

0.1 to 10 g/l hydroxylamine in free or bound form, and

0.1 to 10 g/l of a reducing sugar.

Experience shows that the corrosion prevention and paint adhesion of thecrystalline zinc phosphate layers formed in such a phosphating bath areimproved if the zinc phosphating solution in step (I) additionallycontains one or more of the following cation concentrations:

0.001 to 4 g/l of manganese(II),

0.001 to 4 g/l of nickel(II),

0.002 to 0.2 g/l of copper(II),

0.2 to 2.5 g/l of magnesium(II),

0.2 to 2.5 g/l of calcium(II),

0.01 to 0.5 g/l of iron(II),

0.2 to 1.5 g/l of lithium(I), and

0.02 to 0.8 g/l of tungsten(VI).

The zinc concentration is more preferably in the range between about 0.8and about 1.6 g/l. Zinc concentrations above 1.6 g/l, for examplebetween 2 and 3 g/l, bring only slight advantages for the process, buton the other hand can increase the incidence of sludge in thephosphating bath. Such zinc concentrations are adjusted in a workingphosphating bath if during the phosphating of galvanized surfacesadditional zinc passes into the phosphating bath through its etchingaction. Nickel and/or cobalt ions in a concentration range of in eachcase about 1 to about 50 mg/l for nickel and about 5 to about 100 mg/lfor cobalt in combination with as low a nitrate content as possible, notmore than about 0.5 g/l, improve the corrosion prevention and paintadhesion compared to phosphating baths that do not contain nickel orcobalt or that have a nitrate content of more than 0.5 g/l. In this waya favorable compromise is reached between the performance of thephosphating baths on the one hand and the requirements of the effluenttechnology treatment of the rinse waters on the other hand.

With phosphating baths containing reduced amounts of heavy metals, themanganese content may be in the range from about 0.001 to 0.2 g/l.Otherwise manganese contents of about 0.5 to about 1.5 g/l areconventional.

It is known from DE-A-195 00 927 that lithium ions in amounts of about0.2 to about 1.5 g/l improve the corrosion prevention that can beachieved with zinc phosphating baths. Lithium concentrations in therange from 0.2 to about 1.5 g/l and in particular from about 0.4 toabout 1 g/l also have a beneficial effect on the resultant corrosionprevention with the phosphating process according to the invention andsubsequent post-treatment.

Apart from the aforementioned cations, which are incorporated into thephosphate layer or at least positively influence the crystal growth ofthe phosphate layer, the phosphating baths as a rule also containsodium, potassium and/or ammonium ions to adjust the free acid. The term“free acid” is well known to those skilled in the art in the phosphatingfield. The method chosen to determine free acid as well as the totalacid in this step is specified in the examples. Free acid and total acidrepresent an important control parameter for phosphating baths, sincethey have a large influence on the coating weight. Free acid values ofbetween 0 and 1.5 points in parts phosphating, or up to 2.5 points incoil phosphating, and total acid values of between about 10, or forimmersion phosphating preferably about 15, and about 30 points lie inthe technically normal range and are suitable within the scope of thisinvention.

For the phosphating of zinc surfaces it would not be absolutelynecessary for the phosphating baths to contain so-called accelerators.For phosphating steel surfaces it is, however, necessary for thephosphating solution to contain one or more accelerators. Suchaccelerators are conventionally used in the prior art as components ofzinc phosphating baths. The term accelerators refers to substances thatchemically react with the hydrogen produced on the metal surface by theetching action of the acid in such a way that they are themselvesreduced. Oxidizing accelerators furthermore have the effect of oxidizingiron(II) ions released by the etching action on steel surfaces to thetrivalent oxidation state, so that they can precipitate out as iron(III) phosphate.

In step (II), solutions according to the prior art that produce aconversion layer on aluminum may be used. These solutions must not,however, excessively dissolve the crystalline zinc phosphate layerformed in step (I). The pH of these solutions should therefore lie inthe range from 2.5 to 10, preferably from 3.3 to 10. Advantageously instep (II) solutions are chosen containing components that additionallypassivate the crystalline zinc phosphate layers. Such solutions arementioned hereinafter by way of example. Within the scope of the processsequence according to the invention, in step (II) the metal structuresare generally brought into contact with the treatment solutions byspraying or by dipping. The temperature of the treatment solution forstep (II) is preferably chosen in the range from 20 to 70° C.

By way of example, in step (II) a treatment solution may be used thathas a pH in the range from about 5 to about 5.5 and that containsoverall about 0.3 to about 1.5 g/l of hexafluorotitanate and/orhexafluorozirconate ions. It may be advantageous for the corrosionprotection of the crystalline zinc phosphate layer produced in step (I)if this treatment solution additionally contains about 0.01 to 0.1 g/lof copper ions for step (II).

Moreover, a treatment solution may be used in step (II) that has a pH inthe range from 3.5 to 5.8 and that contains 10 to 500 mg/l of organicpolymers chosen from poly-4-vinylphenol compounds of the immediatelyfollowing general formula (I):

wherein n is an integer between 5 and 100, each of X and Y independentlyof each other denotes hydrogen or a CRR¹OH moiety in which each of R andR¹ independently is hydrogen or an aliphatic or aromatic moiety with 1to 12 carbon atoms.

For step (II) in particular those treatment solutions are preferred thatcontain polyvinylphenol derivatives according to the teaching ofEP-B-319 016. This document also discloses the preparation of suchpolyvinylphenol derivatives. Accordingly, in step (II) a treatmentsolution is preferably used that has a pH in the range from 3.3 to 5.8and contains 10 to 5000 mg/l of organic polymers selected fromhomopolymer or copolymer compounds containing amino groups, comprisingat least one polymer selected from the group consisting of materials (α)and (β), wherein:

(α) consists of polymer molecules each of which has at least one unitconforming to the immediately following general formula (II):

wherein:

each of R² through R⁴ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety with from 1 to 5carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms;

each of Y¹ through Y⁴ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂Cl moiety; an alkyl moiety with from 1 to 18 carbon atoms; an arylmoiety with from 6 to 18 carbon atoms; a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z that conforms to oneof the two immediately following general formulas:

where each of R⁵ through R⁸ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety,a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, anda phosphoalkyl moiety and R⁹ is selected from the group consisting of ahydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxy orpolyhydroxy alkyl moiety, an amino or polyamino alkyl moiety, a mercaptoor polymercapto alkyl moiety, a phospho or polyphospho alkyl moiety, an—O⁻ moiety, and an —OH moiety,

at least one of Y¹ through Y⁴ in at least one unit of each selectedpolymer molecule being a moiety Z as above defined; and

W¹ is selected, independently from one molecule of the component toanother and from one to another unit of any polymer molecule conformingto this formula when there is more than one such unit in a singlepolymer molecule, from the group consisting of a hydrogen moiety, anacyl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety;a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenylethyl moiety; abenzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl,unsubstituted alkylbenzyl; halo or polyhalo alkyl, or halo or polyhaloalkenyl moiety; a moiety derived from a condensation polymerizationproduct of ethylene oxide, propylene oxide or a mixture thereof bydeleting one hydrogen atom therefrom; and a sodium, potassium, lithium,ammonium or substituted ammonium, or phosphonium or substitutedphosphonium cation moiety; and

(β) consists of polymer molecules each of which does not include a unitconforming to general formula (II) as given above but does include atleast one unit corresponding to the immediately following generalformula (III):

wherein:

each of R¹⁰ and R¹¹ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety with from 1 to 5carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms;

each of Y⁴ through Y⁶ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂Cl moiety; an alkyl moiety with from 1 to 18 carbon atoms; an arylmoiety with from 6 to 18 carbon atoms; a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z as defined formaterial (α) above, at least one of Y¹ through Y⁴ in at least one unitof each selected polymer molecule being a moiety Z as above defined; and

W² is selected, independently from one molecule of the component toanother and from one to another unit of any polymer molecule conformingto this formula when there is more than one such unit in a singlepolymer molecule, from the group consisting of a hydrogen moiety, anacyl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety;a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenylethyl moiety; abenzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl,unsubstituted alkylbenzyl; halo or polyhalo alkyl, or halo or polyhaloalkenyl moiety; a moiety derived from a condensation polymerizationproduct of ethylene oxide, propylene oxide or a mixture thereof bydeleting one hydrogen atom therefrom; and a sodium, potassium, lithium,ammonium or substituted ammonium, or phosphonium or substitutedphosphonium cation moiety;

the phrase “polymer molecule” in the above definitions of materials (α)and (β) including any electrically neutral molecule with a molecularweight of at least 300 daltons.

Ordinarily, primarily for reasons of economy, it is preferred to utilizeas materials (α) and/or (β) predominantly molecules which consistentirely, except for relatively short end groups, of units conforming toone of the general formulas (I) and (II) as described above. Againprimarily for reasons of economy, such materials are generally preparedby reacting homopolymers of p-vinyl phenol, for material (α), orphenol-aldehyde condensation products, for material (β), withformaldehyde and secondary amines to graft moieties Z on some of theactivated benzene rings in the materials thus reacted.

However, in some particular instances, it may be more useful to utilizemore chemically complex types of materials (α) and/or (β). For example,molecules formed by reacting a condensable form of a molecule belongingto component (α) or (β) as defined above, except that the moleculereacted need not initially satisfy the requirement for component (α) or(β) that each molecule contain at least one moiety Z, with at least oneother distinct type of molecule which is selected from the groupconsisting of phenols, tannins, novolak resins, lignin compounds,aldehydes, ketones, and mixtures thereof, in order to prepare acondensation reaction product, which optionally if needed is thenfurther reacted with (1) an aldehyde or ketone and (2) a secondary amineto introduce at least one moiety Z as above defined to each molecule, sothat the molecule can qualify as material (α) or (β).

Another example of more complex materials that can be utilized asmaterial (α) is material in which the polymer chains are at leastpredominantly copolymers of simple or substituted 4-vinyl phenol withanother vinyl monomer such as acrylonitrile, methacrylonitrile, methylacrylate, methyl methacrylate, vinyl acetate, vinyl methyl ketone,isopropenyl methyl ketone, acrylic acid, methacrylic acid, acrylamide,methacrylamide, n-amyl methacrylate, styrene, m-bromostyrene,p-bromostyrene, pyridine, diallyidimethyl-ammonium salts, 1,3-butadiene,n-butyl acrylate, t-butylamino-ethyl methacrylate, n-butyl methacrylate,t-butyl methacrylate, n-butyl vinyl ether, t-butyl vinyl ether,m-chlorostyrene, o-chlorostyrene, p-chlorostyrene, n-decyl methacrylate,N,N-diallylmelamine, N,N-di-n-butylacrylamide, di-n-butyl itaconate,di-n-butyl maleate, diethylaminoethyl methacrylate, diethylene glycolmonovinyl ether, diethyl fumarate, diethyl itaconate, diethylvinylphosphate, vinylphosphonic acid, diisobutyl maleate, diisopropylitaconate, diisopropyl maleate, dimethyl fumarate, dimethyl itaconate,dimethyl maleate, di-n-nonyl fumarate, di-n-nonyl maleate, dioctylfumarate, di-n-octyl itaconate, di-n-propyl itaconate, N-dodecyl vinylether, acidic ethyl fumarate, acidic ethyl maleate, ethyl acrylate,ethyl cinnamate, N-ethyl methacrylamide, ethyl methacrylate, ethyl vinylether, 5-ethyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine-1-oxide,glycidyl acrylate, glycidyl methacrylate, n-hexyl methacrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, isobutylmethacrylate, isobutyl vinyl ether, isoprene, isopropyl methacrylate,isopropyl vinyl ether, itaconic acid, lauryl methacrylate,methacrylamide, methacrylic acid, methacrylonitrile,N-methylolacrylamide, N-methylol-methacrylamide,N-isobutoxymethylacrylamide, N-isobutoxy-methylmethacrylamide,N-alkyloxymethylacrylamide, N-alkyl-oxymethylmethacrylamide,N-vinylcaprolactam, methyl acrylate, N-methylmethacrylamide,α-methylstyrene, m-methylstyrene, o-methyl-styrene, p-methylstyrene,2-methyl-5-vinylpyridine, n-propyl methacrylate, sodiump-styrenesulfonate, stearyl methacrylate, styrene, p-styrenesulfonicacid, p-styrenesulfonamide, vinyl bromide, 9-vinyl carbazole, vinylchloride, vinylidene chloride, 1-vinyinaphthalene, 2-vinyinaphthalene,2-vinylpyridine, 4-vinylpyridine, 2-vinylpyridine N-oxide,4-vinylpyrimidine, and N-vinylpyrrolidone.

The following preferences, primarily for reasons of economy, improvedcorrosion resistance, and/or increased water solubility, apply,independently for each preference, to the molecules of materials (α) and(β):

each of R² through R⁶, R¹⁰, R¹¹, W¹, and W², independently for each andfrom one unit to another in the same or a different molecule, preferablyis a hydrogen moiety;

each of Y¹ through Y⁶, independently for each and from one unit toanother in the same or a different molecule, preferably is a hydrogenmoiety or a moiety Z;

each polymer molecule contains a number of units corresponding to one ofgeneral formulas (II) and (III) as defined above that is at least, withincreasing preference in the order given, 2, 3, 4, 5, 6, 7, or 8 andindependently preferably is not more than 100, 75, 50, 40, 30, or 20,

in the total of materials (α) and (β) in a composition used in step (II)according to the invention, the number of moieties Z has a ratio to thenumber of aromatic nuclei that is at least, with increasing preferencein the order given, 0.01:1.0, 0.03:1.0, 0.05:1.0, 0.10:1.0, 0.20:1.0,0.40:1.0, 0.50:1.0, 0.60:1.0, 0.70:1.0, 0.80:1.0, 0.90:1.0, or 0.95:1.0and independently preferably is not more than, with increasingpreference in the order given, 2.0:1.0, 1.6:1.0, 1.50:1.0, 1.40:1.0,1.30:1.0, 1.20:1.0, 1.10:1.0, or 1.00:1.0; and

in the total of materials (α) and (β) in a composition used in step (II)according to the invention, the number of “polyhydroxy moieties Z”,which are defined as moieties Z in which at least one of R⁵ through R⁸in the general formulas given above for moieties Z has (i) from 3 to 8,or preferably from 4 to 6, carbon atoms and (ii) as many hydroxylgroups, each attached to one of the carbon atoms, as one less than thenumber of carbon atoms in the R⁵ through R⁸ moiety, has a ratio to thetotal number of moieties Z in the composition that is at least, withincreasing preference in the order given, 0.10:1.0, 0.20:1.0, 0.30:1.0,0.40:1.0, 0.50:1.0, 0.60:1.0, 0.70:1.0, 0.80:1.0, 0.90:1.0, or 0.98:1.0(preparation of such materials is described in the references citedabove).

Poly(5-vinyl-2-hydroxy-N-benzyl)-N-methylglucamine is a specific polymerof the most preferred type, which, in the acidic pH range which is to beestablished, is present at least in part as an ammonium salt.

Solutions may be used that do not contain any further activeconstituents, apart from the polyvinyl phenol derivative and an acid foradjusting the pH, preferably phosphoric acid. Additions of furtheractive constituents, in particular hexafluorotitanate orhexafluorozirconate ions, may however improve the layer formation onaluminum. For example, a solution may be used whose pH lies preferablyin the range from about 3.3 to about 5.8 and which contains as organicpolymer about 100 to about 5000 mg/l of an organic polymer in the formof a methylethanolamine derivative or N-methylglucamine derivative ofpolyvinyl phenol and in addition 10 to 2000 mg/l of phosphate ions, 10to 2500 mg/l of hexafluorotitanate or hexafluorozirconate ions, and 10to 1000 mg/l of manganese ions.

Instead of the polyvinyl phenol derivatives, whose preparation involvesa certain expense, there may be used in step (II) solutions ordispersions of organic polymers selected from homopolymers and/orcopolymers of acrylic acid and methacrylic acid as well as their esters.Preferably these solutions or dispersions have pH values in the rangefrom about 3.3 to about 4.8 and contain about 250 to about 1500 mg/l oforganic polymers. According to the teaching of EP-B-0 08 942 thesepolymer solutions or dispersions may additionally containhexafluorotitanates, hexafluorozirconates and/or hexafluorosilicates.

EXAMPLES

A process sequence according to the invention was tested on sample metalsheets of cold rolled steel (hereinafter usually abbreviated as “CRS”),electrolytically galvanized steel (hereinafter usually abbreviated as“ZE”), electrolytically zinc-iron-coated steel (hereinafter usuallyabbreviated as “ZFE”) and on aluminum 6111. As is conventional in theautomobile manufacturing sector, these metal sheets were first of allcleaned with alkali and activated with an activating solution containingtitanium phosphate. The sheets were then dipped for 3 minutes in aphosphating bath at a temperature of 48° C. having the followingcomposition:

Zn=1.2 g/l

Mn=0.8 g/l

Ni=0.8 g/l

PO₄ ³⁻=18 g/l

NO₂—=110 ppm

Residual cations=Na⁺

Free acid 1.1

Sealed phosphate layers having coating weights in the region of 2 g/m²were deposited by this phosphating procedure on cold rolled steel,electrolytically galvanized steel and on electrolyticallyzinc-iron-coated steel. Scanning electron microscopy photographs showedthat only widely-scattered zinc phosphate crystals had formed on thealuminum sheets.

As step (II) the sample sheets were treated with fully deionized water(comparison tests) as well as with solutions of one of the followingcompositions (a), (b), and (c). These solutions had a temperature of 25°C. and were sprayed for 30 seconds onto the sample sheets. The sheetswere then sprayed for 15 seconds with fully deionized water and blowndry with compressed air at room temperature. For the corrosionprevention tests, they were coated with a triple layer paint structure,applied in the order shown: E-coat=PPG ED 5000, base coat=Dupont white542 AB 839, Clear coat=Dupont RK 8010. The corrosion resistance testswere carried out according to the GM9540P-B process cycle of GeneralMotors, which consists of the following steps:

1. (1.1) Spraying each panel with a salt spray solution (0.9 wt. % oftable salt, 0.1 wt. % of calcium chloride, 0.25 wt. % of sodiumbicarbonate, with the balance water) sufficiently to thoroughly wet thepanel; (1.2) within 30 minutes after spraying the panel, inserting itinto an atmosphere controlled to remain at 25° C. and 30-50% relativeatmospheric humidity; (1.3) ninety minutes after beginning step (1.2),removing the panel from the controlled atmosphere in which it was keptduring step (1.2), then repeating steps (1.1) and (1.2) three timeseach. Step 1 as a whole thus consumes 8 hours.

2. 8 hours' condensate water test at 49° C. and 95-100% relativeatmospheric humidity;

3. 8 hours' dry storage at 60° C. and <30% relative atmospherichumidity;

4. At the week-end: only dry storage at 25° C. and 30-50% relativeatmospheric humidity.

The steps 1 to 3 immediately above in each case form a cycle that isrepeated Mondays through Fridays. Step 4 is not counted in the cyclenumber. The tests lasted for 40 cycles (5 cycles per week correspondingto a test time of 8 weeks).

Table 1 below shows the compositions of the three post-rinse solutions,and Tables 2 and 3 show the zinc phosphate coating etch amounts and theaverage paint creepages at the scribe (full scribe width) respectively.

TABLE 1 POST-RINSE COMPOSITIONS Amount of Ingredient in: Post-rinsePost-rinse Post-rinse soln.(a), soln.(b), soln.(c), Ingredient pH 2.7 pH3.5 pH 2.9 Polymer* 0.453 g/l 0.451 g/l 0.113 g/l Phosphate 0.957 g/l0.955 g/l 0.239 g/l Hexafluortitanate 1 g/l 1 g/l 0.25 g/l Mn(II) 0.39g/l 0.39 g/l 0.1 g/l *Poly(5-vinyl-2-hydroxy-N-benzyl)-N-methylglucamine

TABLE 2 ZINC PHOSPHATE COATING ETCHING LOSS VALUES Test Post-RinseCoating Loss, Number Substrate Solution Percent Example 1 CRS (a) 69Example 2 CRS (b)  5 Example 3 CRS (c) 27 Example 4 ZE (a) 50 Example 5ZE (b)  5 Example 6 ZE (c) 31 Example 7 ZFE (a) 50 Example 8 ZFE (b)  1Example 9 ZFE (c) 25

TABLE 3 CORROSION TEST RESULTS Test Post-Rinse Paint Creepage, NumberSubstrate Solution Millimeters Comparison 1 CRS Deionized Water 9.6Example 1 CRS (a) 8.8 Example 2 CRS (b) 3.1 Example 3 CRS (c) 4.2Comparison 2 ZE Deionized Water 2.2 Example 4 ZE (a) 1.6 Example 5 ZE(b) 1.8 Example 6 ZE (c) 1.8 Comparison 3 ZFE Deionized Water 2.2Example 7 ZFE (a) 1.3 Example 8 ZFE (b) 1.6 Example 9 ZFE (c) 1.1Comparison 4 Al6111 Deionized Water 1.7 Example 10 Al6111 (a) 0.9Example 11 Al6111 (b) 1.2 Example 12 Al6111 (c) 1.2

What is claimed is:
 1. A process for chemical pretreatment, before anorganic coating, of a composite metal structure that contains at leastone aluminium or aluminium alloy portion together with at least onesteel, galvanized steel or alloy-galvanized steel portion, said processcomprising steps of: I) treating in a first step the composite metalstructure with a zinc phosphating solution, wherein the zinc phosphatingsolution has a free acid value of between 0 and 2.5 points and containsan amount of free fluoride, expressed in g/l, that is not greater than aquotient of the number 8 divided by the solution temperature in ° C. fora sufficient time to thereby form on steel and on galvanized andalloy-galvanized steel a surface-covering crystalline zinc phosphatelayer having a coating weight in the range from 0.5 to 5 g/m², butwithout forming a surface-covering zinc phosphate layer on the aluminiumportions; and subsequently, with or without an intermediate rinsing withwater, (II) contacting in a second step the composite metal structurewith a treatment solution, comprising organic polymer,hexafluorotitanate and/or hexafluorozirconate ions, having a DH of2.5-10 and a temperature in a range from 20 to 70° C. such that thetreatment solution does not dissolve more than 60% of the crystallinezinc phosphate layer on steel, galvanized and/or alloy-galvanized steel,but does produce a conversion layer on the aluminum portions.
 2. Aprocess according to claim 1, wherein: in step (I) the zinc phosphatingsolution has a pH in a range from 2.5 to 3.6 and a temperature in arange from 20 to 65° C. and contains an amount of free fluoride,expressed in g/l, that is not greater than a quotient of the number 8divided by the solution temperature in ° C.; from 0.3 to 3 g/l ofZn(II), from 5 to 40 g/l of phosphate ions, and at least one of thefollowing amounts of the following types of accelerators: 0.3 to 4 g/lof chlorate ions, 0.01 to 0.2 g/l of nitrite ions, 0.05 to 2 g/l ofm-nitrobenzenesulfonate ions, 0.05 to 2 g/l of m-nitrobenzoate ions,0.05 to 2 g/l of p-nitrophenol, 0.001 to 0.15 g/l of hydrogen peroxidein free or bound form, 0.1 to 10 g/l hydroxylamine in free or boundform, and 0.1 to 10 of reducing sugar; and optionally, one or more ofthe following 0.001 to 4 g/l of manganese (II) 0.001 to 4 g/l of nickel(II), 0.002 to 0.2 g/l of copper (II), 0.2 to 2.5 g/l of magnesium (II),0.2 to 2.5 g/l of calcium (II), 0.01 to 0.5 g/l of iron (II), 0.2 to 1.5g/l of lithium (I), and 0.02 to 0.8 g/l of tungsten (VI) and in step(II) the treatment solution does not dissolve more than 25% of thecrystalline zinc phosphate layer deposited in step (I).
 3. A processaccording to claim 2, wherein the treatment solution used in step (II)has a pH in the range from 3.5 to 5.5 and comprises from 0.3 to 1.5 g/lof hexafluorotitanate ions, hexafluorozirconate ions, or both.
 4. Aprocess according to claim 3, wherein the treatment solution used instep II) additionally comprises from 0.01 to 0.1 g/l of copper ions. 5.A process according to claim 2, wherein the treatment solution used instep (II) has a pH in the range from 3.3 to 5.8 and contains at leaseone of: from 10 to 500 mg/l of organic polymers chosen frompoly-4-vinylphenol molecules that conform to the immediately followinggeneral formula (I):

wherein n is a integer between 5 and 100, each of X and Y independentlyof each other denotes hydrogen or a CRR¹OH moiety in which each of R andR¹ independently is hydrogen or an aliphatic or aromatic moiety with 1to 12 carbon atoms; from 10 to 5000 mg/l of organic polymers selectedfrom materials (α) and (β), where: (α) consists of polymer moleculeseach of which has at least one unit conforming to the immediatelyfollowing general formula (II):

wherein: each of R² to R⁴ is selected, independently for each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety with from 1 to 5carbon atoms, or an aryl moiety with from 6 to 18 carbon atoms; each ofY¹ through Y⁴ is selected, independently for each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂Cl moiety; an alkyl moiety with from 1 to 18 carbon atoms; an arylmoiety with from 6 to 18 carbon atoms, a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z that conforms to oneof the two immediately following general formulas:

where each of R⁵ through R⁸ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety,a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, anda phosphoalkyl moiety and R⁹ is selected from the group consisting of ahydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxy orpolyhydroxy alkyl moiety, an amino or polyaminoalkyl moiety, a mercaptoor polymercapto alkyl moiety, a phosphor or polyphospho alkyl moiety, an—O⁻ moiety, OH moiety, at least one Y¹ or Y⁴ in at least one unit ofeach selected polymer molecule being a moiety Z as above defined; and W¹is selected, independently from one molecule of the component to anotherand from one to another unit of any polymer molecule conforming to thisformula when there is more than one such unit in a single polymermolecule, from the group consisting of a hydrogen moiety, an acrylmoiety, an acetyl moiety, a benzoyl moiety, a 3-allyloxy-2-hydroxypropylmoiety; a 3-benzyloxy-2-hydroxypropyl moiety; a 3-butoxy-2-hydroxypropylmoiety; a 3-alkyloxy-2-hydroxypropyl moiety; a 2-hydroxyoctyl moiety; a2-hydroxyalkyl moiety; a 2-hydroxy-2-phenylethyl moiety; a2-hydroxy-2-alkylphenylethyl moiety; a benzyl, methyl, ethyl, propyl,unsubstituted alkyl, unsubstituted allyl, unsubstituted alkyl-benzyl;halo or polyhalo alkyl; or halo or polyhalo alkenyl moiety, a moietyderived from a condensation polymerization product of ethylene oxide,propylene oxide or a mixture thereof by deleting one hydrogen atomtherefrom; and a sodium, potassium, lithium, ammonium or substitutedammonium, or phosphonium or substituted phosphonium cation moiety; and(β) consists of polymer molecules each of which does not include a unitconforming to general formula (II) as given above but does include atleast one unit corresponding to the immediately following generalformula (III);

wherein: R¹⁰ and R¹¹ is selected, independently for each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety with from 1 to 5carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms; each ofY⁴ through Y⁶ is selected, independently of each other and independentlyfrom one molecule of the component to another and from one to anotherunit of any polymer molecule conforming to this formula when there ismore than one such unit in a single polymer molecule, except as notedfurther below, from the group consisting of; a hydrogen moiety; a —CH₂Clmoiety; an alkyl moiety with from 1 to 18 carbon atoms; an aryl moietywith from 6 to 18 carbon atoms; a moiety conforming to the generalformula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selected from thegroup consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety,a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, anda phosphoalkyl moiety; and a moiety Z as defined for material (α) above,at least one of Y¹ through Y⁴ in at lease one unit of each selectedpolymer molecule being a moiety Z as above defined; and W₂ is selected,independently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an acyl moiety, an acetyl moiety,a benzoyl moiety; a 3-allyloxy-2-hydroxypropyl moiety; a3-benzyloxy-2-hydroxypropyl moiety; a 3-butoxy-2-hydroxypropyl moiety; a3-alkyloxy-2-hydroxypropyl moiety; a 2-hydroxyoctyl moiety; a2-hydroxyalkyl moiety; a 2-hydroxy-2-phenylethyl moiety; a2-hydroxy-2-alkylphenylethyl moiety, a benzyl; methyl, ethyl, propyl,unsubstituted alkyl, unsubstituted alkyl, unsubstituted alkylbenzyl;halo or polyhalo alkyl, or halo or polyhalo alkenyl moiety; a moietyderived from a condensation polymerization product of ethylene oxide,propylene oxide or a mixture thereof by deleting one hydrogen atomtherefrom; and a sodium, potassium, lithium, ammonium or substitutedammonium, or phosphonium or substituted phosphonium cation moiety; andfrom 250 to 1500 mg/l of organic polymers selected from the groupconsisting of homopolymers and copolymers of acrylic acid, methacrylicacid, and esters of acrylic and methacrylic acids, the phrase “polymermolecule” in the above definitions of materials (α) and (β) includingany electrically neutral molecule with a molecular weight of at least300 daltons.
 6. A process according to claim 5, wherein the treatmentsolution used in step (II) comprises from 10 to 5000 mg/l of organicpolymers selected from materials (α) and (β) and at least 20 number % ofthe moieties Z in material (α) and material (β) in the treatmentsolution used in step (II) of the process are polyhydroxyl moieties Z.7. A process according to claim 5, wherein the treatment solution usedin step (II) of the process comprises, as material (α), a condensationreaction produce of (i) polyvinyl phenol having a weight averagemolecular weight in a range from 1000 to 10,000 (ii) formaldehyde orparaformaldehyde and (iii) at least one secondary organic amine.
 8. Aprocess according to claim 7, wherein the secondary organic amine isselected from the group consisting of methylethanolamine,N-methylglucamine, and mixtures thereof.
 9. A process according to claim8, wherein the treatment solution has a pH in the range from 3.3 to 4.8,contains 100 to 5000 mg/l of the condensation reaction product, and inadditionally comprises: from 10 to 2000 mg/l of phosphate ions, from 10to 2500 mg/l of hexafluorotitanate ions, hexafluorozirconate ions, orboth; and from 10 to 1000 mg/l of manganese ions.
 10. A processaccording to claim 1, wherein the treatment solution used in step (II)has a pH in a range from 3.5 to 5.5 and comprises from 0.3 to 1.5 g/l ofhexafluorotitanate ions, hexafluorozirconate ions, or both.
 11. Aprocess according to claim 10, wherein the treatment solution used instep (II) additionally comprises from 0.01 to 0.1 g/l of copper ions.12. A process according to claim 1, wherein the treatment solution usedin step (II) has a pH in the range from 3.3 to 5.8 and contains at leastone of: from 10 to 500 mg/l of organic polymers chosen frompoly-4-vinylphenol molecules that conform to the immediately followinggeneral formula (I):

wherein n is an integer between 5 and 100, each of X and Y independentlyof each other denotes hydrogen or a CRR¹OH moiety in which each of R andR¹ independently is hydrogen or an aliphatic or aromatic moiety with 1to 12 carbon atoms; from 10 to 5000 mg/l of organic polymers selectedfrom materials (α) and (β), where: (α) consists of polymer moleculeseach of which has at least one unit conforming to the immediatelyfollowing general formula (II):

wherein: each of R² through R⁴ is selected, independently from onemolecule of the component to another and from one to another unit of anypolymer molecule conforming to this formula when there is more than onesuch unit in a single polymer molecule, from the group consisting of ahydrogen moiety, an alkyl moiety with from 1 to 5 carbon atoms, and anaryl moiety with from 6 to 18 carbon atoms; each Y¹ through Y⁴ isselected, independently of each other and independently from onemolecule of the component to another and from one to another unit of anypolymer molecule conforming to this formula when there is more than onesuch unit in a single polymer molecule, except as noted further below,from the group consisting of: a hydrogen moiety; a —CH₂Cl moiety; analkyl moiety with from 1 to 18 carbon atoms; an aryl moiety with from 6to 18 carbon atoms; a moiety conforming to the general formula—CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selected from the groupconsisting of a hydrogen moiety, an alkyl moiety, an aryl moiety, ahydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, and aphosphoalkyl moiety; and a moiety Z that conforms to one of the twoimmediately following general formulas:

where each of R⁵ through R⁸ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety,a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, anda phosphoalkyl moiety and R⁹ is selected from the group consisting of ahydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxy orpolyhydroxy alkyl moiety, an amino or polyaminoalkyl moiety, a mercaptoor polymercapto alkyl moiety, a phospho or polyphospho alkyl moiety, an—O⁻ moiety, and an —OH moiety, at least one Y¹ through Y⁴ in at leastone unit of each selected polymer molecule being a moiety Z as abovedefined; and W1 is selected, independently from one molecule of thecomponent to another and from one to another unit or any polymermolecule conforming to this formula when there is more than one suchunit in a single polymer molecule, from the group consisting of ahydrogen moiety, an acryl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety;a 3-butoxy-2-hydroxypropyl moiety, a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkyphenyl-ethyl moiety; abenzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl,unsubstituted alkylbenzyl, halo or polyhalo alkyl, or halo or polyhaloalkenyl moiety; a moiety derived from a condensation polymerizationproduct of ethylene oxide, propylene oxide or a mixture thereof bydeleting one hydrogen atom therefrom; and a sodium, potassium, lithium,ammonium or substituted ammonium, or phosphonium or substitutedphosphonium cation moiety; and (β) consists of polymer molecules each ofwhich does not include a unit conforming to general formula (II) asgiven above but does include at least one unit corresponding to theimmediately following general formula (III):

wherein: each of R¹⁰ and R¹¹ is selected, independently of each otherand independently from one molecule of the component to another and fromone to another unit of any polymer molecule conforming to this formulawhen there is more than one such unit in a single polymer molecule, fromthe group consisting of a hydrogen moiety, an alkyl moiety with from 1to 5 carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms;each of Y⁴ through Y⁶ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂C1 moiety; an alkyl moiety with from 1 to 18 carbon atoms, an arylmoiety with from 6 to 18 carbon atoms; a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z as defined formaterial (α) above, at least one of Y¹ through Y⁴ in at least one unitof each selected polymer molecule being a moiety Z as above defined; andW2 is selected, independently from one molecule of the component toanother and from one to another unit of any polymer molecule conformingto this formula when there is more than one such unit in a singlepolymer molecule, from the group consisting of a hydrogen moiety, anacryl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety;a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenyl-ethyl moiety;a benzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstitutedallyl, unsubstituted alkyl-benzyl; halo or polyhalo alkyl, or halo orpolyhalo alkenyl moiety; a moiety derived from a condensationpolymerization product of ethylene oxide, propylene oxide or a mixturethereof by deleting one hydrogen atom therefrom; and a sodium,potassium, lithium, ammonium or substituted ammonium, or phosphonium orsubstituted phosphonium cation moiety; and from 250 to 1500 mg/l oforganic polymers selected form the group consisting of homopolymers andcopolymers of acrylic acid, methacrylic acid, and esters of acrylic andmethacrylic acids, the phrase “polymer molecule” in the abovedefinitions of materials (α) and (β) including any electrically neutralmolecule with a molecular weight of at least 300 daltons.
 13. A processaccording to claim 12, wherein the treatment solution used in step (II)comprises from 10 to 5000 mg/l of organic polymers selected frommaterials (α) and (β) and at least 20 number % of the moieties Z inmaterial (α) and material (β) in the treatment solution used in step(II) of the process are polyhydroxyl moieties Z.
 14. A process accordingto claim 12, wherein the treatment solution used in step (II) of theprocess comprises, as material (α), a condensation reaction product of(i) polyvinyl phenol having a weight average molecular weight in a rangefrom 1000 to 10,000, (ii) formaldehyde or paraformaldehyde, and (iii) atleast one secondary organic amine.
 15. A process according to claim 14,wherein the secondary organic amine is selected from the groupconsisting of methylethanolamine, N-methylglucamine, and mixturesthereof.
 16. A process according to claim 15, wherein the treatmentsolution has a pH in the range from 3.3 to 4.8, contains 100 to 5000mg/l of the condensation reaction product, and additionally comprises:from 10 to 2000 mg/l of phosphate ions; from 10 to 2500 mg/l ofhexafluorotitanate ions, hexafluorozirconate ions, or both; and from 10to 1000 mg/l of manganese ions.
 17. A process according to claim 1,wherein the treatment solution used in step (II) has a pH In the rangefrom 3.3 to 5.8 and contains from 10 to 5000 mg/l of organic polymersselected from materials (α) and (β), where: (α) consists of polymermolecules each of which has at least one unit conforming to theimmediately following general formula (II):

wherein: each of R² through R⁴ is selected, independently of each otherand independently from one molecule of the component to another and fromone to another unit of any polymer molecule conforming to this formulawhen there is more than one such unit in a single polymer molecule, fromthe group consisting of a hydrogen moiety, an alkyl moiety with from 1to 5 carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms;each of Y¹ through Y⁴ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂Cl moiety; an alkyl moiety with from 1 to 18 carbon atoms; an arylmoiety with from 6 to 18 carbon atoms; a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z that conforms to oneof the two immediately following general formulas:

where each of R⁵ through R⁸ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, from thegroup consisting of a hydrogen moiety, an alkyl moiety, an aryl moiety,a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkyl moiety, anda phosphoalkyl moiety and R⁹ is selected from the group consisting of ahydrogen moiety, an alkyl moiety, an aryl moiety, a hydroxy orpolyhydroxy alkyl moiety, an amino or polyaminoalkyl moiety, a mercaptoor polymercapto alkyl moiety, a phospho or polyphospho alkyl moiety, an—O⁻ moiety, an —OH moiety, at least one Y¹ through Y⁴ in at least oneunit of each selected polymer molecule being a moiety Z as abovedefined; and W¹ is selected, independently from one molecule of thecomponent to another and from one to another unit of any polymermolecule conforming to this formula when there is more than one suchunit in a single polymer molecule, from the group consisting of ahydrogen moiety, an acyl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety,a 3-butoxy-2-hydroxypropyl moiety, a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety, a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenylethyl moiety; abenzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl,unsubstituted alkylbenzyl; halo or polyhalo alkyl, or halo or polyhaloalkenyl moiety; a moiety derived from a condensation polymerizationproduct of ethylene oxide, propylene oxide or a mixture thereof bydeleting one hydrogen atom therefrom; and a sodium, potassium, lithium,ammonium or substituted ammonium, or phosphonium or substitutedphosphonium cation moiety; and (β) consists of polymer molecules each ofwhich does not include a unit conforming to general formula (II) asgiven above but does include at least one unit corresponding to theimmediately following general formula (III):

wherein: each of R¹⁰ and R¹¹ is selected, independently of each otherand independently from one molecule of the component to another and fromone to another unit of any polymer molecule conforming to this formulawhen there is more than one such unit in a single polymer molecule, fromthe group consisting of a hydrogen moiety, an alkyl moiety with from 1to 5 carbon atoms, and an aryl moiety with from 6 to 18 carbon atoms;each of Y⁴ through Y⁶ is selected, independently of each other andindependently from one molecule of the component to another and from oneto another unit of any polymer molecule conforming to this formula whenthere is more than one such unit in a single polymer molecule, except asnoted further below, from the group consisting of: a hydrogen moiety; a—CH₂Cl moiety; an alkyl moiety with from 1 to 18 carbon atoms, an arylmoiety with from 6 to 18 carbon atoms; a moiety conforming to thegeneral formula —CR¹²R¹³OR¹⁴, where each of R¹² through R¹⁴ is selectedfrom the group consisting of a hydrogen moiety, an alkyl moiety, an arylmoiety, a hydroxyalkyl moiety, an aminoalkyl moiety, a mercaptoalkylmoiety, and a phosphoalkyl moiety; and a moiety Z as defined formaterial (α) above. At least one of Y¹ through Y⁴ in at least one unitof each selected polymer molecule being a moiety Z as above defined; andW² is selected, independently from one molecule of the component toanother and from one to another unit of any polymer molecule conformingto this formula when there is more than one such unit in a singlepolymer molecule, from the group consisting of a hydrogen moiety, anacryl moiety, an acetyl moiety, a benzoyl moiety; a3-allyloxy-2-hydroxypropyl moiety; a 3-benzyloxy-2-hydroxypropyl moiety;a 3-butoxy-2-hydroxypropyl moiety; a 3-alkyloxy-2-hydroxypropyl moiety;a 2-hydroxyoctyl moiety; a 2-hydroxyalkyl moiety; a2-hydroxy-2-phenylethyl moiety; a 2-hydroxy-2-alkylphenylethyl moiety; abenzyl, methyl, ethyl, propyl, unsubstituted alkyl, unsubstituted allyl,unsubstituted alkyl-benzyl; halo or polyhalo alkyl, or halo or polyhaloalkenyl moiety; a moiety derived from a condensation polymerizationproduct of ethylene oxide, propylene oxide or a mixture thereof bydeleting one hydrogen atom therefrom; and a sodium, potassium, lithium,ammonium or substituted ammonium, or phosphonium or substitutedphosphonium cation moiety; and At least 20 number % of the moieties Z inmaterial (α) and (β) in the treatment solution used in step (II) of theprocess are polyhydroxyl moieties Z, the phrase “polymer molecule” inthe above definitions of materials (α) and (β) including anyelectrically neutral molecule with a molecular weight of at least 300daltons.
 18. A process accordingly to claim 17, wherein the treatmentsolution used in step (II) of the process comprises, as material (α), acondensation reaction produce of (i) polyvinyl phenol having a weightaverage molecular weight in a range from 1000 to 10,000, (ii)formaldehyde or paraformaldehyde, and (iii) at least one secondaryorganic amine.
 19. A process according to claim 18, wherein thesecondary organic amine is selected from the group consisting ofmethylethanolamine, N-methylglucamine, and mixtures thereof.
 20. Aprocess according to claim 19, wherein the treatment solution has a pHin the range from 3.3 to 4.8, contains 100 to 5000 mg/l of thecondensation reaction product, and additionally comprises: from 10 to2000 mg/l of phosphate ions; from 20 to 2500 mg/l of hexafluorotitanateions, hexafluorozirconate ions, or both; and from 10 to 1000 mg/l ofmanganese ions.
 21. A process for chemical pretreatment, before anorganic coating, of a composite metal structure that contains at leastone aluminium or aluminium alloy portion together with at least onesteel, galvanized steel or alloy-galvanized steel portion, said processcomprising steps of: I) treating in a first step the composite metalstructure with a zinc phosphating solution having a free acid value ofbetween 0 and 2.5 points and an amount of free fluoride, expressed ing/l, that is not greater than a quotient of the number 8 divided by thesolution temperature in ° C., at a temperature in a range from 20 to 65°C. for a time sufficient to deposit on the steel, galvanized andalloy-galvanized steel portion, a surface-covering crystalline zincphosphate layer and deposit on the aluminium portions only widelyscattered zinc phosphate crystals; and subsequently, with or without anintermediate rinsing with water, II) contacting in a second step thecomposite metal structure with a treatment solution, comprising organicpolymer, hexafluorotitanate and/or hexafluorozirconate ions, having a pHof 2.5-10 and a temperature in a range from 20 to 70° C. such that thetreatment solution does not dissolve more than 60% of the crystallinezinc phosphate layer on steel, galvanized and/or alloy-galvanized steel,but does produce a conversion layer on the aluminum portions.
 22. Aprocess for chemical pretreatment, before an organic coating, of acomposite metal structure that contains at least one aluminium oraluminium alloy portion together with at least one steel, galvanizedsteel or alloy-galvanized steel portion, said process comprising stepsof: I) treating in a first step the composite metal structure with azinc phosphating solution, wherein the zinc phosphating solution has apH in a range from 2.5 to 3.6 and a temperature in a range from 20 to65° C. and contains an amount of free fluoride, expressed in g/l, thatis not greater than a quotient of the number 8 divided by the solutiontemperature in ° C. thereby forming on steel and on galvanized andalloy-galvanized steel a surface-covering crystalline zinc phosphatelayer having a coating weight in the range from 0.5 to 5 g/M2, butwithout forming a zinc phosphate layer on the aluminum portions; andsubsequently, with or without an intermediate rinsing with water, II)contacting in a second step the composite metal structure with atreatment solution, comprising organic polymer, hexafluorotitanateand/or hexafluorozirconate ions, having a pH of 2.5-10 and a temperaturein a range from 20 to 70° C. such that the treatment solution does notdissolve more than 60% of the crystalline zinc phosphate layer on steel,galvanized and/or alloy-galvanized steel, but does produce a conversionlayer on the aluminum portions.